1. Field of the Invention
This invention relates to a semiconductor device of high reliability. More particularly, it relates to a semiconductor device which comprises a passivation layer of high performance made of a silicon nitride material.
2. Brief Description of the Prior Art
Semiconductor devices of which high reliabilities are required, especially ICs and LSIs for telecommunications to be used in computers, etc. and for industries to be used in car electronics, etc. have heretofore been mainly sealed in ceramic packages. Since, however, the ceramic packages are expensive, the use of inexpensive plastic packages (resin-molded) has recently been contrived. This is because the automation of operations and the batch assembly are easily carried forward and also because a resin forming the material of the plastic package is cheaper.
The resin used for the plastic package, however, often contains impurity ions therein and is also unsatisfactory in point of airtightness in such a manner that moisture in the outside penetrates therethrough. The device within the plastic package is, therefore, liable to undergo variations in characteristics, corrosion of Al interconnections, etc. In order to compensate for these disadvantages of the resin material and to maintain the high reliability of the device, an excellent passivation layer needs to be disposed on the semiconductor body. The passivation layer in this case is required to be free from defects such as pinholes and cracks and to be excellent in the ability to stop the moisture as well as the impurity ions.
Heretofore, a phosphosilicate glass film and a silicon dioxide film have chiefly been employed as the passivation layers of LSIs etc. These films, however, are low in mechanical strength, so that when the semiconductor devices are sealed into the plastic packages, cracks appear in the passivation layer films due to compressive stresses at the hardening of the resin. The appearance of the cracks in the passivation layer is unfavorable because the impurity ions contained in the sealing resin and the moisture which penetrates through the sealing resin intrude into circuit elements of the device through the cracks to give rise to the degradation of the characteristics of the device and the breaking of the interconnections due to corrosion, resulting in lowering the reliability of the device.
The following references are cited to show the state of the art:
(i) Japanese Patent Application Laying-open No. 56973/1978 PA1 (ii) Japanese Patent Application Publication No. 21017/1969 PA1 (iii) P. H. Holloway and H. J. Stein: Journal of Electrochemical Society, vol. 123, No. 5 (May 1976), pages 723-728.